Is the big bang theory just for how our universe began?

No.

The big bang is the expansion of the universe. It may or may not be related to the origin of its components.

The evidence found so far does not indicate the origin of the components for the universe, nor does the evidence tell us anything of events occurring before its expansion. Rather than repeatedly reciting this qualifying sentence, the big bang is often simply referred to (incorrectly) as the beginning or "creation" of the universe. Television documentaries do not bother to make the distinction. Though not technically correct, for most practical discussions of the physics of the universe, this is okay. For discussions on the origin of the universe, the error is unacceptable.

Guesses and ideas on the origin of the universe are plentiful but unsubstantiated. There are many religions that have their own explanation although most reject all other explanations but their own.

Although some suggestions have the start of the big bang as the start of the universe, I don't know of any scientific requirement for or against an infinitely long past.

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The Big Bang Theory is just for how our universe began, and it has overwhelming empirical evidence supporting it. There may be other universes, as part of a multiverse. We may never know.

There are many well-respected physicists, such as Stephen Hawking, Lawrence Krauss, Sean M. Carroll, Victor Stenger, Michio Kaku, Alan Guth, Robert A.J. Matthews, and Nobel laureate Frank Wilczek, who have created scientific models where the Big Bang and thus the entire universe could arise from nothing but a quantum vacuum fluctuation -- via natural processes.

For more, watch the video at the 1st link - "A Universe From Nothing" by Lawrence Krauss.

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so a strategies as i know, the great bang concept is the only concept customary by ability of scientists that explains the beginning of the universe. assorted medical observations help the great bang hypothesis of cosmic beginning inclusive of: -Cosmic history radiation that equals what's mathematically predicts by ability of the great bang kind -Measurable Redshifting reasons by ability of galaxies shifting far flung from one yet another at severe speeds. that is named the Hubble enlargement. -Experimentally measured relative abundance of the primordial factors of helium-4, helium-3, deuterium, and lithium-7 to Hydrogen experience what's envisioned by ability of the great bag kind different proposals for the beginning of the universe are generally non secular in nature, and as a result are ideals, not theories. Theories ought to be testable and open to alter. non secular beginning myths are as a result not theories.

It applies only to the observations we see in *this* universe.

See my blog.